Answer:
Scientist applied heat and antimicrobial treatment to sewage samples and then observed that nitrate was no longer formed in that conditions (in absence of bacteria).
Step-by-step explanation:
The first step to prove anything is to actually build a hypothesis to explain why a natural phenomenon occurs.
In this particular case, microbial ecologists knew that hydrogen gas is oxidized in soil and that ammonia is oxidized in sewage as they this can be observed and measured directly by them chemically.
Then, they built and hypothesis of what could be happening that led to the oxidized of ammonia into the soil. One possibility, among others, is to postulate (hypothesize) that microbial metabolism is responsible for the ammonia being oxidized in sewage.
Indeed, at least one experiment must be done to test this hypothesis. For example, one would eliminate microbial from sewage; then:
- if the hypothesis is correct, no nitrate (produced by ammonia oxidation) would be no longer formed. In absence of the producer agent (bacteria), no product (nitrate) is expected. To eliminate these specialized bacteria one would apply heat and antimicrobial treatment to sewage. As a result, if by eliminating the bacteria no nitrate is formed, bacteria were for sure related to its formation.
- if the hypothesis is incorrect, in absence of bacteria, nitrate would be still be formed, proving that bacteria are not responsible for producing it.
In real world, ecologist did this experiment and obtained that no nitrate is formed when bacteria are removed from siege.